In December, North Korea announced that it had test-launched an Unha-3 rocket. / Korean Central News Agency via AP

by Michael Winter, USA TODAY

by Michael Winter, USA TODAY

The people charged with managing crises in Yokohama, Japan, created a mini-crisis Wednesday morning by erroneously announcing on Twitter that North Korea had launch a missile.

It took 20 minutes for one of the agency's 40,000 Twitter followers to call and point out the mistake, The Japan Times reported. The tweet was deleted immediately and the agency apologized.

Japan has been on alert since North Korea threatened nuclear war against its neighbors and the United States. Amid the saber-rattling, Pyongyang said it would test-launch a mobile ballistic missile, which Tokyo said it would shoot down if it passed over Japanese territory.

Japan's early warning system would alert local governments about the likely flight path immediately to local governments concerned, and Yokohama officials had prepared an announcement in the event of a launch. But about 11 a.m. local time (10 p.m. ET Tuesday), a city worker tweeted the mistaken missile missive.

"We will further look into why this kind of thing happened, and will make sure there will be no recurrence," a city official said.